1. Field of the Invention
The present invention relates to a method for laminating disc-shaped substrates, more particularly to such a method of integrally laminating two disc-shaped substrates using an adhesive sheet, and more specifically to such a method for laminating both the two disc-shaped substrates together as a unit.
2. Prior Art
In recent years, computers, especially personal computers have remarkably popularized on one hand, the capacity of storage mediums to be used therein, especially, the capacity of a storage disc has been highly densified more and more and types thereof have been also increased accompanied thereby on the other hand.
There are a magnetic disc-shaped, an optical disc (e.g., CD-ROM), an optical disc (e.g., MO), etc. as the storage disc. Among others, the demand for the optical disc has been increased recently.
Take, for example, an optical disc so called xe2x80x9cDVDxe2x80x9d, a disc-shaped substrate in the form of single plate which constitutes it is standardized as a thickness of 0.6 mm, an outer diameter of 120 mm, and an inner diameter 15 mm in its central hole.
Since such a thin disc-shaped substrate formed of a single plate is low in mechanical strength and is easily deformable, and in view of storage capacity, the disc-shaped substrates each of the same thickness (0.6 mm) are bonded onto each other to form an integrated substrate in a practical use thereof.
Such a high density storage disc-shaped (i.e. a DVD) is generally used as a ply-plate structure as set forth above, but is not used as a single plate. In such a case, it is necessary that both the upper and lower disc-shaped substrates to be bonded onto each other.
For manufacturing an integrated optical disc by bonding two single plates, there is provided a method of integrally laminating the two single plates by use of an adhesive agent.
According to such method, UV cured resin as the adhesive agent is coated to the lower disc-shaped substrate in the form of a doughnut, with the upper disc-shaped substrate being placed thereupon to rotate both the disc-shaped substrates to thereby develop or draw the UV cured resin.
After such development or orientation, irradiation of UV is applied to cure UV cured resin interposed between both the disc-shaped substrates together as a unit.
However, such method relies on development or orientation by means of rotation so that, not only UV cured resin may be scattered outwardly to have the periphery thereof dirty or contaminated but also the resin may be dispersed to lessen effective usage to afford a lesser yield rate of UV cured resin.
A step or the like of irradiating UV for curing the adhesive agent is required to thus increase manufacturing processes thus increasing manufacturing cost.
Under such circumstances, a new laminating method with use of the adhesive agent, which requires no development or orientation process of the adhesive agent.
According to a new and useful method, an adhesive sheet member is employed instead of UV cured resin (adhesive agent).
More specifically, this is such a method that the adhesive agent as an adhesive sheet member is bonded to the lower disc-shaped substrate, with the upper disc-shaped substrate being overlaid thereon, and that these disc-shaped substrates are pressurized by a pressing body from above to integrate them as a unit.
Notwithstanding, due to the fact that the adhesive agent tends to instantaneously adhere to both the disc-shaped substrates, air bubbles are readily entered between the adhesive agent and the disc-shaped substrates when the adhesive sheet is pressed against the surface of the lower disc-shaped substrate. This is the also the case where the upper disc-shaped substrate is laid on the lower disc-shaped substrate to which the adhesive agent adheres. As a result, the optical disc with air bubbles may be inevitably manufactured to thus impede or deteriorate the quality.
The present invention has been provided to solve the foregoing problem. In other words, it is an object of the invention to provide a method for laminating disc-shaped substrates between which there is extremely lesser bubbles or without any bubble.
As a result of a concentrate study to solve the aforementioned problem, there has been an awareness that once both the laminated disc-shaped substrates are left to or exposed to a high-pressure atmosphere to afford volume reduction thereby leading to a new and useful invention.
Stated otherwise, a first aspect of the invention resides in a method for laminating disc-shaped substrates wherein both the disc-shaped substrates has been left to high-pressure atmosphere for a given time after the substrates have been laminated by an adhesive agent.
A second aspect of the invention resides in a method of laminating disc-shaped substrates wherein an upper disc-shaped is pressed against a lower disc-shaped substrate by a pressing body simultaneously with leaving the same to the high-pressure atmosphere.
A third aspect of the invention resides in a method of laminating disc-shaped substrates comprising the following sequential four steps of;
1) bonding the adhesive agent to the surface of the lower disc-shaped substrate,
2) placing the upper disc-shaped substrate on the adhesive applied to low disc-shaped substrate,
3) pressurizing the upper disc-shaped substrate against the lower disc-shaped substrate by means of the pressing body, and
4) exposing both the disk-shaped substrates to a high-pressure atmosphere.
A fourth aspect of the invention resides in the method wherein the adhesive agent is bonded to the surface of the lower disc-shaped substrate, and wherein the step is taken to bond the adhesive agent to the surface of the lower disc-shaped substrate in such a manner that the adhesive-backed sheet is pressed against the substrate from one end to the other end.
A fifth aspect of the invention resides in the method wherein the step of 3) in the third aspect of the invention is performed in a state where the upper disc-shaped substrate is pressurized against the lower disc-shaped substrate by means of the pressing body in a state whereas the pressing body is held against in such a manner that a contact portion may be magnified from the center side to the outside.
A sixth aspect of the invention resides in the method wherein firstly the pressing body in the step of (4) is held against the upper disc-shaped substrate in such a manner that a contact portion may be magnified from the center side to the outside,
A seventh aspect of the invention resides in the method wherein hold down pressure not only in the step (1) but also in the step (3) in the third aspect of the invention is applied to magnify high-pressure.
With the employment of the method of laminating disc-shaped substrates according to the first to the seventh aspect of the invention, each of air bubbles may be of smaller size to obtain high quality optical disc.